The disclosure of Japanese Patent Application No. 2000-325455 filed on Oct. 25, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to techniques associated with a dust cover to be attached to a shock absorber used in a suspension mechanism of an automotive vehicle. More particularly, the present invention is concerned with a novel dust cover assembly that permits an easy and firmly attachment thereof to the shock absorber without looseness thereof, a method of producing the dust cover assembly, and a product equipped with the dust cover assembly.
2. Description of the Related Art
There is known a shock absorber used in a suspension system of an automotive vehicle, which is interposed between and fixed to a member on the side of a body of the vehicle and a member on the side of a wheel of the vehicle so as to damp or attenuate a vibrational load applied from the wheel to the body of the vehicle. The shock absorber includes a cylinder filled with a fluid and a piston rod reciprocally slidably received by the cylinder. In the known shock absorber, a tubular dust cover is employed in order to cover a fluid-tight sealing portion between the cylinder and the piston rod. The dust cover is disposed radially outwardly of the shock absorber so as to cover a substantially entire area of a part of the piston rod that is protruded from the cylinder.
In general, the tubular dust cover is mounted on the shock absorber. For instance, JP-U-57-1927 discloses a first example of known mounting structures in which the tubular dust cover is press-fitted at its upper axial open end portion on an outer circumferential surface of a bound stopper. Further, JP-A-8-261267 discloses a second example of known mounting structures in which a tubular dust cover made of a synthetic resin material is press-fitted at its upper axial open end portion on a fixing metal member which is fixed to a protruding end portion of the piston rod of the shock absorber.
However, the first example of the known mounting structures may give an adverse effect on the elastic property of the bound stopper, and may cause an disengagement of the dust cover from the bound stopper upon elastic deformation of the bound stopper. The second example of the known mounting structure does not ensure a firmly engagement between the dust cover made of a synthetic resin material and the rigid fixing metal member, so that the dust cover needs to be forcedly pressed on the fixing metal member by means of a snap ring or the like in order to prevent disengagement of the dust cover from the fixing metal member. This results in an increase of the number of required components and a resultant cumbersome manufacturing process. In addition, the dust cover fixed by the snap ring is likely to come loose or be disengaged from the fixing member, whereby the dust cover tends to contact or interfere with the other components, possibly causing wound or injury of the dust cover and/or other components and undesirable impact noise. In the second example of the known mounting structure, it has been proposed to employ a rubber dust cover in order to ensure the easy and firmly attachment of the dust cover to the fixing metal member. However, the rubber dust cover inevitably suffers from a problem of secular change of its property due to ozone contained in a surrounding atmosphere. This leads to a reduced elastic force of the dust cover and occurrence of ozone cracks in the rubber dust cover, possibly causing a disengagement of the dust cover from the fixing metal member. Therefore, the known mounting structures for mounting the dust cover on the shock absorber are still insufficient to ensure the ease and firmly attachment of the dust cover to the shock absorber.
It is therefore one object of this invention to provide a dust cover assembly having a dust cover made of a synthetic resin material, which permits an easy and firmly attachment of the dust cover to the shock absorber without looseness thereof.
It is another object of this invention to provide a method of producing such a dust cover assembly which permits easily and firmly attached of a dust cover to the shock absorber.
It is yet another object of this invention to provide a shock absorber equipped with such a dust cover assembly.
The above and/or other objects may be attained according to at least one of the following aspects of the invention. The following preferred forms of the respective aspects of the invention may be adopted at any possible optional combinations. It is to be understood that the present invention is not limited to the following forms or combinations of these forms, but may otherwise be recognized based on the thought of the present invention that described in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
According to one aspect of the invention, it is provided a method of producing a dust cover assembly having a tubular dust cover disposed radially outwardly of a shock absorber for covering a protruding part of a piston rod of the shock absorber, said method comprising the steps of: (a) preparing a fixing member including a mounting bore to which a protruding end portion of the piston rod is inserted and fixed, and an engaging portion formed in an outer circumferential surface thereof and having an undercut shape in an axial direction thereof; (b) preparing a tubular parison having a large diameter portion at one of axially opposite end portion thereof; (c) positioning the parison with respect to the fixing member such that the large diameter portion of the parison is disposed radially outwardly of the outer circumferential surface of the fixing member including the engaging portion; (d) closing a blow mold so as to form a mold cavity around the parison and so as to hold the large diameter portion of the parison in close contact with the outer circumferential surface of the fixing member for molding the large diameter portion of the parison; and (e) executing a blow molding of the parison by introducing a compressed gas into the blow mold through the mounting bore of the fixing member, so as to form the tubular dust cover.
According to this method of the invention, when the blow molding is executed for producing the dust cover, one of the axially opposite end portions of the parison is pressed onto and held in close contact with or stick firmly to the outer circumferential surface of the fixing member including the engaging portion by the blow mold, so that one of axially opposite end portion of the dust cover is formed on and covers the outer circumferential surface of the fixing member. It is noted that the engaging portion of the fixing member has an undercut shape in the axial direction of the fixing member, in other words, the engaging portion is retracted radially inwardly from other portions of the fixing member which are located axially opposite sides of the engaging portion. The present method ensures that one of axially opposite end portions of the dust cover integrally formed with the other part of the dust cover is formed on and stick firmly to the outer circumferential surface of the radially retracted engaging portion of the fixing member, at the same time when the other part of the dust cover is produced by blow molding.
Accordingly, the present method makes it possible to fixedly mount the dust cover on the fixing member simultaneous with the blow molding of the dust cover, without requiring a special facilities or process of mounting the dust cover on the fixing member, resulting in an improved efficiency of assembling of the dust cover with the shock absorber. The present method is able to form the dust cover to be held in close contact with the outer circumferential surface of the fixing member, thus preventing looseness or disengagement of the dust cover from the fixing member at the interface between the dust cover and the fixing member, and preventing undesirable entrance of muddy water or the like into the dust cover with high stability, while assuring high fluid-tight sealing at the interface between the dust cover and the fixing member.
Moreover, the diameter of the parison is increased only at its axial end portion to be fixedly mounted on the fixing member. This arrangement facilitates a process of disposing the parison radially outwardly on the fixing member, and ensures a sufficient amount of inflation of the diameter of the parison upon blow molding the parison, making it possible to form the dust cover having a relatively small wall-thickness. For instance, the present method is able to produce with high stability the dust cover having a wall-thickness of not larger than 2.0 mm, by using commodity plastics, while minimizing occurrence of burrs.
According to one preferred form of the present method, the large diameter portion of the parison is formed by increasing a diameter of the one of axially opposite end of the parison. This method enables to thin the wall thickness of the large diameter portion of the parison, making it possible to form the dust cover on the outer circumferential surface of the fixing member with a sufficiently small wall thickness, while minimizing occurrence of burrs on the surface of the dust cover.
According to another preferred form of the present method, the fixing member is positioned and supported by a jig which protrudes axially outwardly from the fixing member, and the blow mold has a cutting protrusion, the cutting protrusion of the blow mold being brought into abutting contact with an outer circumferential surface of a portion of the jig, which portion is located axially outward of the fixing member, upon closing the blow mold, in order to cut the one of axially opposite end portion of the parison by and between the cutting protrusion and the jig, so that the fixing member is covered by the dust cover over a substantially entire area of the outer circumferential surface thereof. This method enables to form the dust cover so as to be held in contact with and cover the substantially entire area of the outer circumferential surface of the fixing member, thus preventing looseness of the dust cover from the fixing member at the interface between the dust cover and the fixing member, and the undesirable entrance of muddy water or the like into the dust cover, with further improved stability.
According to yet another preferred form of the present method, the fixing member has a bound stopper holding portion open to one of axially opposite sides thereof, the method further comprising the step of: assembling the bound stopper to the bound stopper holding portion of the fixing member, before disposing the parison radially outwardly of the outer circumferential surface of the fixing member. This method permits an easy assembling of the dust cover with the fixing member, while eliminating a cumbersome process of setting the bound stopper in the fixing member disposed inside of the dust cover through a relatively long bore of the dust cover. Upon executing the blow molding, a predetermined amount of compressed gas may be introduced into the parison through a bore of the bound stopper through which the piston rod is extended. This means that the bound stopper, which is assembled with the fixing member before mounting the dust cover on the fixing member, gives no adverse effect on efficiency of the blow molding of the dust cover.
According to another aspect of the invention, it is provided a shock absorber comprising, a dust cover assembly produced by the above described method according to the one aspect of the invention. This shock absorber prevents occurrence of looseness of the dust cover and a resultant contact or interfere of the dust cover with other components that generates undesirable impact noises. Further, the manufacture and assembling of the dust cover is effectively simplified, leading to a reduced manufacturing cost and an improved commodity value of the shock absorber.
According to yet another aspect of the invention, it is provided a dust cover assembly disposed radially outwardly of a shock absorber for covering a protruding portion of a piston rod of said shock absorber, the dust cover assembly comprising: a dust cover having a tubular shape; and a fixing member connectable to a protruding end portion of the piston rod and including a cup-shaped first metal holder and a cup-shaped second metal holder whose diameter is larger than that of the first metal holder, the first and second metal holders being superposed on and connected to each other at outer surfaces of their bottom wall portions, the first metal holder arranged for holding a rubber mount which is adapted to be held in elastic contact with a body of a vehicle, the second metal holder arranged for holding a bound stopper, one of axially opposite open end portions of the dust cover being attached to the fixing member such that the one of axially opposite open end portions of the dust cover is held in close contact with an outer circumferential surface of the second metal holder and at least a part of an outer circumferential surface of the first metal holder.
In this aspect of the invention, the one axial end portion of the dust cover is engaged with and held in contact with the portion formed between the bottom wall potions of the first and second metal holder which are superposed on and fixed to each other. This makes it possible to firmly fix and support the dust cover to and by the fixing member, while ensuring a high fluid-tight sealing between the dust cover and the fixing member.
Preferably, the dust cover is held in contact with not only the outer circumferential surface of the second metal holder but also a substantially entire area of the outer circumferential surface of the first metal holder. This ensuring further improved fluid-tight sealing between the dust cover and the fixing member.
Preferably, the dust cover may be formed by blow molding, although the dust cover may be formed by an injection molding in which a predetermined resin material is injected into a mold cavity of a mold in which the fixing member is set in a predetermined position. Since the blow molding enables to form the desired dust cover with a sufficiently small wall thickness, with high stability. Upon executing the blow molding, the large diameter portion of the parison formed at its one axial end portion is desirably held in close contact with the outer circumferential surface of the fixing member by closing and pressing the mold onto the fixing member with the large diameter portion of the parison interposed therebetween.
Further, the first metal holder may be dimensioned to have a diameter smaller than that of the second metal holder. In this arrangement, the outer surface of the bottom wall portion of the second metal holder serves as the engaging portion formed as a relatively large undercut portion in the axial direction of the fixing member, to which the dust cover is firmly adhered. Thus, the dust cover is fixedly supported by the fixing member with excellent stability.
Preferably, the first metal holder includes an outward flange integrally formed at its open end portion so as to extend radially outwardly. The dust cover may be held in contact with and cover an surface of the outward flange, whereby the dust cover is fixedly supported by the fixing member with further improved stability.